1. Field of the Invention
The invention relates to an assembly for selectively preventing the linear motion of a lancet in a device for producing a drop of blood for blood sampling.
2. Description of Related Art
Lancets are used to pierce the skin of a patient, usually through the finger. Blood then flows through the incision where it is collected for testing in a blood collection tube such as a capillary tube or pipette.
Historically, early lancets generally had a handle and a sharp lancet tip extending therefrom. However, numerous problems are inherent with such lancets such as controlling the depth and angle of penetration by the lancet tip, controlling the force of the insertion, and the psychological affect to the user of seeing the exposed lancet tip.
One attempt to avoid these and other problems with this early type of lancet was to create lancets having lancet tips that are spring loaded to be injected into and removed from the patient's skin in a linear direction. Typically, these devices hide the lancet tip both before and after the incision is made to prevent its view by the patient, to minimize trauma to the patient and to prevent inadvertent contact with the lancet. Examples of such a lancet injector are disclosed in U.S. Pat. No. 4,580,565 issued on Apr. 8, 1986 and its parent application U.S. Pat. No. 4,503,856, issued on Mar. 12, 1985, both of which are issued to W. D. Cornell and C. Evans and assigned to the assignee of the present invention.
Other examples of lancet devices that move the lancet tip in a linear direction into and out of contact with a patient's tissue are disclosed in U.S. Pat. No. 4,924,879 issued to W. J. O'Brien on May 15, 1990 and U.S. Pat. No. 5,196,025 issued to Ranalletta et al. on Mar. 23, 1993. In the O'Brien device, the lancet tip moves by being acted upon by a connecting rod connected to the outer edge of a rotating wheel. As the wheel rotates, the lancet tip is moved in a reciprocating fashion. The lancet tip is constrained to linear motion by a pair of rollers positioned on either side of the lancet.
In the Ranalletta device, the lancet tip is moved by the straightening of a pair of pivoting arms. The pivoting arms are normally aligned at an angle with respect to each other. As the arms are straightened, the lancet tip is moved. The lancet tip is constrained to linear movement by a guide bore that conformably holds and positions the lancet.
The lancet body is preferably sterilized at the time of manufacture. In many devices a cap surrounds and encases the distal tip of the lancet. The cap prevents inadvertent contact with the distal tip of the lancet and also preserves the sterility of the lancet tip. The cap is placed over and sealed to the lancet body to preserve the sterile condition of the distal tip of the lancet until the cap is removed prior to the use of the device.
The cap is usually simultaneously molded with the lancet body so that a break point connects the cap with the lancet body. The break point is usually a narrowed portion of the material of the cap and the lancet body. The break point breaks when the cap is twisted. The cap is then removed from around the distal tip of the lancet to expose the sharp pointed distal tip of the lancet.
None of the devices having a cap covering the distal tip of the lancet have means to prevent the lancet from moving out of the lancet device until it is desired to use the lancet device.